1. Field of the Invention
The present invention generally relates to the fabrication of semiconductor devices, and more particularly, the present invention relates to the fabrication of semiconductor memory devices having storage node electrodes.
A claim of priority is made to Korean Patent Application No. 10-2005-0096165, filed on Oct. 12, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
2. Description of the Related Art
Semiconductor devices, for example, dynamic random access memory (DRAM) devices, continued to become more highly integrated with increased capacity. One way in which the degree of integration is increased is by disposing larger numbers of capacitors within a small area while at the same time increasing the capacitance of each capacitor. This can be achieved, for example, by increasing the density and height of storage node electrodes of the capacitors.
For example, U.S. Pat. No. 6,855,597 by Shin, Chul-Ho, et al. discloses a DRAM cell having a cylindrical or concave storage node electrode. Dielectric layers of the DRAM cell are formed on both an inner surface and an outer surface of the storage node electrode. Thus, the area of the dielectric layers is increased, and the capacitance of a capacitor is increased. However, due to the increase in density of the DRAM cell, adjacent storage node electrodes may contact each other (known as ‘bridging’) when outer surfaces of the storage node electrodes are exposed. Bridging of the storage node electrodes can cause device errors.
FIG. 1 is a cross-sectional view illustrating a conventional DRAM device, and FIG. 2 is a plan view of a bottom surface of a storage node electrode of the conventional DRAM device of FIG. 1.
Referring to FIGS. 1 and 2, storage node electrodes 70 are provided on an etch stop film 65, and may be connected to a semiconductor substrate 50 using contact plugs 60 provided within an interlayer insulating film 55. Although other shapes are possible, in this example the storage node electrodes 70 are formed in the form of a rigid beam of a rectangular parallelepiped. The storage node electrodes 70 may be exposed by removing a mold insulating film (not shown) encompassing their outer surfaces. However, in removing the mold insulating film, adjacent storage node electrodes 70 may contact each other due to surface tension of a water film or a water mark 90 caused by water contained in a wet solution or provided in a washing or drying operation.
More specifically, two kinds of forces may be applied between the storage node electrodes 70. One is a surface tension (Fs) that works to attract the storage node electrodes 70 to each other, and the other one is an elastic force (Fe) that is works in a direction opposite to that of surface tension.
A bridge between the storage node electrodes 70 occurs when the surface tension (Fs) is greater than the elastic force (Fe). As shown in the following Expression 1, the probability (P) of a bridge may be obtained from the equilibrium of the surface tension (Fs) and the elastic force (Fe).P∝2v sin θ(L+H)H3/3EID  (Expression 1)where, E denotes Young's modulus, I denotes the inertia momentum of a horizontal section, H denotes a height of the storage node electrodes 70, v denotes the surface tension coefficient of water, θ denotes a contact angle between the storage node electrodes 70 and the water film or the water mark 90, D denotes a separation distance between the storage node electrodes 70, and L denotes a width of the storage node electrode 70.
Accordingly, it can be seen from the proportional relationship shown in Expression 1 that the bridge probability (P) is proportional to the height (H) of the storage node electrodes 70, and is inversely proportional to the separation distance (D). However, it is generally desirable to increase the height (H) of the storage node electrodes 70 to improve the capacitance, and to decrease the separation distance (D) between the storage node electrodes 70 to increase density, both of which will result in an increase in bridge probability (P). In other words, as the DRAM device becomes more highly integrated with increased capacity, the bridge probability (P) of Expression 1 increases.
FIGS. 3 and 4 are photographic images of storage node electrodes 70 of a conventional DRAM device. Referring to these figures, bridges are observed between the storage node electrodes 70 within an encircled region A of the images. Bridging of this type can cause electrical shorts between adjacent capacitor nodes, which in turn can result in device failures.
Returning to FIG. 1, it should also be noted that the conventional method of fabricating the DRAM device may also be disadvantageous in that voids may occur by corrosion of a material under the storage node electrodes 70, for example, the contact plugs 60. The voids can occur when bottom portions of the storage node electrodes 70 are exposed to a wet solution, and are known as being caused by so-called galvanic corrosion. Like bridging, voids of this type can degrade the reliability of the DRAM device.